I am also in the same problem than the rest of the people posting in this thread and I am fully sympathetic. I find PayPal lack of care upseting. There is however a way around this problem by setting the notify_url and then follow PayPal procedure for verifying the IPN post. For PHP languaje you can read about this in: http://stackoverflow.com/questions/4848227/validate-that-ipn-call-is-from-paypal Check the answer by Sergey Shuchkin, which is the lastest one. This is also in PayPal documentation
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